Childhood Obesity's Invisible Cousin: Poor Bone Development

Iowa study shows that activity in early years is key to strong bones.

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Everyone knows about the child and teen obesity problem. You only have to walk into a school to see it. What you won’t notice is a serious problem lurking below the surface.

Research has shown that bone development increases dramatically in the early and teen years. After adolescence, it is difficult to significantly increase bone strength.

You can begin exercising at age 35, and dramatically improve your cardiac fitness and muscle strength. The same doesn’t apply to the bones; it’s too late. The bone strength that goes undeveloped in the early years can lead to osteoporosis many decades later.

The Iowa Bone Development Study recently measured activity levels and bone strength gains of 530 Iowa youth from age 5 to age 17. Accelerometers were used over several years to measure the subjects’ activity levels. A number of different bone measurements were taken to assess not just bone mass, but overall bone strength.

The results showed a significant difference in bone strength between boys and girls who were highly active from ages 5 to 9 compared to those who exercised less during the same period. Those who exercised more had stronger, healthier bones.

A separate analysis revealed the “trajectory” of subject activity levels over the 12-year period. At age 17, the girls were moving roughly 75 percent less than they had at age 5. “These results suggest that by late adolescence, nearly all girls are not optimizing the known benefits of physical activity to bone health,” the study authors report in the British Journal of Sports Medicine. Only six percent of all 17-year-old girls were meeting recommendations for daily moderate to vigorous activity.

The 17-year-old boys exercised about twice as much as the girls (40 minutes a day vs. 20 minutes), but few met recommended levels. The boys’ activity levels increased from age 5 to age 8, then declined dramatically. For girls, there was no peak at age 8. Their activity levels fell in a straight line from age 5 to age 17.

“This study indicates that high levels of childhood physical activity are positively associated with bone strength in late adolescence even after drastic reductions in physical activity during puberty,” the research team concludes. “The bone health benefits of physical activity are not being realized due to low levels of activity for most youth, especially girls.”

See our kids running section for resources on how to get and keep children running in a way that's healthy for and appealing to them.

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